An ideal PWM-VSI inverter using only one current sensor in the DC-link

This paper describes how to improve the performance of open loop, low cost PWM-VSI controlled AC machines by the use of one current sensor. The performance is especially improved at low speed where nonlinearities like blanking-time and voltage drop are dominant. An often used modulation technique is described and basic compensation techniques are presented. Only one current sensor in the DC link is used for reconstruction of all three phase currents and the currents are used for compensation. Different limitations are discussed. The compensation techniques are tested in a 16-bit microcontroller based inverter. Tests show that the phase currents can be reconstructed by measurement of the DC link current both at low and high speed. They also show that a highly improved torque-speed characteristic can be obtained by using the compensation techniques and an almost ideal inverter is obtained. >